Hitherto, a coated type magnetic recording medium has been widely used. Such coated type medium has been prepared by dispersing a ferromagnetic powder such as oxides, e.g., .gamma.-Fe.sub.2 O.sub.3, Co-doped .gamma.-Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, Co-doped Fe.sub.3 O.sub.4, bertholide compounds of .gamma.-Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4 or CrO.sub.2, or ferromagnetic alloy mainly comprising transition metals such as Co, Ni or Fe in an organic binder such as a copolymer of vinyl chloride and vinyl acetate, a copolymer of styrene and butadiene, an epoxy resin or a polyurethane resin, coating the resulting magnetic coating composition on a non-magnetic support, followed by orientation and drying.
In recent years, attention has been drawn to a thin metal film type magnetic recording medium having a magnetic recording layer of a ferromagnetic thin metal film which is prepared, without using an organic binder, by a vapour deposition method such as vacuum deposition as described in U.S. Pat. Nos. 4,354,908, 4,343,834, 4,245,008, 4,074,016, etc., sputtering as described in U.S. Pat. Nos. 3,856,579, 3,625,849, etc. or an ion plating as described in U.S. Pat. Nos. 3,898,952, 3,929,604, 4,002,546, etc. or a plating method such as an electric plating method as described in U.S. Pat. Nos. 2,927,889, 3,578,571, etc. or an electroless plating method as described in U.S. Pat. Nos. 4,072,781, 4,128,691, 4,250,225, etc. Various attempts have been made to put the products made by these methods into practical use due to the increased demand for high density magnetic recording.
In a conventional coated type magnetic recording medium, metal oxides having low saturation magnetization are mainly used as a magnetic material, and the content of the magnetic material in the coated type magnetic recording layer is about 30 to 50% by volume. Therefore, the currently used magnetic recording medium has reached its limit with respect to high output and high density recording. In addition, the manufacturing steps of coated type magnetic recording media are complicated and large auxiliary equipment is necessary to recover solvents or to prevent air pollution. On the other hand, the thin metal film type magnetic recording media are advantageous in that an extremely thin film of ferromagnetic metal having much higher saturation magnetization than magnetic composition of oxides can be formed without using non-magnetic materials such as an organic binder. With recent developments in high density magnetic recording technique, gap length of the magnetic head for recording and reproducing has narrowed to less than 1.0 .mu.m and recording depth in the magnetic recording layer has become shallower. As a result, a thin metal film type magnetic recording medium in which the total thickness of the magnetic recording layer can be used for high output and high density recording. Of thin metal film type magnetic recording media, the magnetic recording medium having a magnetic recording layer prepared by vacuum deposition is more advantageous since the magnetic layer can be formed rapidly; the manufacturing process is relatively simple and the medium can be prepared by a dry process which does not necessitate disposing of waste solutions.
However, the vapour deposition type magnetic recording media still have problems, in particular low durability of the magnetic thin film. That is, the magnetic thin film is subjected to relative contact movement with a magnetic head during recording and reproducing magnetic signals and thus is very likely worn out and broken. Therefore, a magnetic recording layer of the magnetic recording medium must have a mechanical strength sufficient to endure contact movement with a magnetic head. However, the mechanical strength of the magnetic recording film formed by a conventional vapour deposition process is still unsatisfactory.